The present invention relates to a hydraulic piston and a process for its surface treatment in order to achieve desired properties with respect to wear resistance and corrosion resistance at the surface of the piston.
Hydraulic pistons for use in hydraulic brake systems are e.g. known from the field of automotive vehicle brakes. The pistons exhibit a specially designed surface in order to satisfy requirements, above all, with respect to wear resistance and corrosion resistance. To safeguard these requirements, customary hydraulic brake pistons for application in friction brakes are frequently chrome-plated on their surface. Both the risk of detachment of the chrome-plating and the chrome-plating""s lack in environmental friendliness is found to be a shortcoming. For other coating materials, too, there is the problem of insufficient adherence to the actual piston material so that the piston surface may easily be damaged. In addition, any coating applied will cause undesirable changes in the outside dimensions of the pistons.
DE 31 14 124 A1 further describes a piston for combustion engines which is made of aluminum and silicon and includes a hard oxidized bottom. Due to the employment of cost-intensive materials, the surface treatment of the bottom is also sophisticated, what makes the completed piston relatively expensive. An additional disadvantage can be seen in the fact that the piston has an improved surface quality only in partial areas. Thus, the corrosion resistance is not ensured for use of the piston as a hydraulic piston.